Electroluminescent devices comprise electroluminescent material that is capable of emitting light when a current is passed through it. The material used for electroluminescent devices can be light emitting polymers or small organic molecules. Organic devices may, for example, be OLEDs. For activating electroluminescent devices, a current is applied to the electroluminescent material by means of electrodes.
More specifically, electroluminescent devices, such as OLEDs, comprise electroluminescent material disposed between electrodes. Upon application of a suitable voltage, current flows through the electroluminescent material from an anode to a cathode. Light is produced by radiative combination of holes and electrons inside the electroluminescent material.
Electroluminescent devices using organic electroluminescent material for general illumination have a forward voltage in the range of the 2 to 5 V. This low voltage makes it unsuitable for direct driving at general-purpose alternating current (AC) electric power supplies (i.e. mains). One solution of this problem is to connect as many OLED devices in series as it is required to achieve the required resistance of the electronic circuit. The problems which such kind of circuit are that the OLED peak current is much higher than the average value, so that mains current harmonics might exceed regulation limits and the OLED average and peak current values vary greatly within the mains voltage variation.
Another possible solution is an electrical circuitry known as ballast circuit or load circuit that is required to operate the OLED devices directly from mains. The ballast or load circuit converts the AC voltage of the public grid to a form which is suitable to drive an OLED light source at a prescribed lightness. Conventional alternating current OLED devices thus may comprise segmented OLEDs and distributed thin film resistive structures serving as electrical ballast or load to operate the OLEDs directly from mains, i.e., without expensive electronic driver circuits.
However, while such conventional segmented electroluminescent devices are not very flexible with regard to power distribution, they are specially designed for best electrical performance. Sometimes it may be desirable to use only standard components (i.e. OLEDs and resistors) or ballast circuits which cannot be integrated as simple thin film structures.